1. Field of the Invention
The invention relates generally to vehicle positioning methods and apparatus, such as vehicle stops and particularly to positioning stops known as truck push rolls and methods of positioning trucks by use of such truck push rolls. Such truck push rolls may be used in locating the rear of a material dump truck with respect to a dump location and particularly with respect to a continuously advancing dump location, for example, a feed hopper of a roadway paving machine.
2. Discussion of the Prior Art
Paving apparatus for laying down continuous strips of pavement necessarily requires a continuous supply of paving material. Typically, trucks deliver the material to the paving site. According to one preferred manner of operation, supply trucks with unloading provisions, such as tiltable beds, back up against a feed or supply hopper located at a front end of a paving machine or paver. When the rear of the truck bed is properly positioned with respect to the front of the feed hopper, the bed is raised and the paving material, such as asphaltic aggregate material, is transferred to the feed hopper of the paver.
Construction equipment, such as dump trucks, paving machines or similar type of apparatus are typically constructed for rugged use. Thus typically the equipment does not include bumpers, or even shock absorbing bumpers, as may have been provided for automobiles or even boat hulls for docking purposes. The intent of such shock absorbing bumpers is to protect the respective vehicle from damage due to contact with another object. The typical ruggedness with which the construction apparatus of interest has been regarded as not needing shock absorbing bumpers to afford such equipment protection from damage. A prior art problem of positioning trucks with respect to the feed hopper in the absence of bumpers was solved to accommodate the needs of the supply operation performed while the paving machine is constantly advancing.
The truck typically remains in position with respect to the feed hopper of the paver only while the material is being dumped into the hopper and immediately thereafter drives off to give way to the next truck. The change-over time between trucks is preferably minimized to optimize the time allocated to actually dumping the material into the feed hopper. Thus to quickly position each of the trucks with respect to the feed hopper, a truck positioning device known as truck push rolls is mounted to the front of the feed hopper of the respective machine to which the material is being transferred. Such push rolls are horizontally disposed rolls which are spaced to coincide with the track width of the trucks.
There are two types of state of the art push roll assemblies, push rolls with so called "truck hooks" and those without. The function of truck hooks is well known in the art. Truck hooks are retainers of trucks which typically engage both outer rear wheels of a truck in a clamshell type manner after the truck has become positioned against the push rolls. The hooks may be engaged manually, by overcentering mechanisms, or by hydraulic cylinders in a direct or remote operation. On level roadways and even on slight descending slopes, roughness of base grades may provide sufficient frictional resistance to retain supply trucks against push rolls, such that the use of truck hooks becomes unnecessary. Also, during the brief stop of a supply truck against a positioning stop, such as a push roll assembly, a truck operator may apply a slight pressure on the vehicle's brakes to maintain contact with the push rolls. In the further discussion of the invention and its background, it should be understood that problems addressed by the current invention relate to positioning the trucks. The current invention consequently applies equally to push roll assemblies with and without the so-called truck hooks.
Thus, in both instances, trucks back their wheels against the rolls which remain in contact with the truck wheels while the truck is dumping its load of material. A support structure of the rolls is typically pinned to the frame at the leading edge of the respective machine to allow a pivoting movement about a vertical axis through the centerline of the machine to allow for some misalignment of a truck backing into the rolls. The rolls consequently provide a simple apparatus for repetitively establishing and maintaining minimum spacing between the rear of the trucks and the front edge of the feed hopper. In case of an asphalt paving machine, as the paving machine advances, the truck is pushed forward and advances in an apparently fixed relationship with the paving machine, hence at a constant spacing with respect to feed hopper. The material supplied by each truck allows the paver to advance but a short distance in its operation and frequent truck exchanges at the front of such feed hopper become a necessary operation to sustain a continuous paving process.
While state of the art push rolls allow the supply trucks to quickly position themselves with respect to the feed hopper to unload the material, the sudden contact by the tires of the loaded trucks appears to be the cause of a possible problem. The problem may be more severe when the drivers of the supply trucks are attempting to deliver the load of material in the shortest possible time. It appears that paving defects may be caused by the sudden impacts between the rear wheels of a fully loaded material supply truck and the push rolls. Considered to be defects are abrupt changes in the density of the material being paved, such as voids or bumps. They are believed to be caused when the screed of a paver is being jarred. Also, a sudden change in the forward speed of the paver may be the cause of such imperfections or paving defect.
Another inherent deficiency with state of the art push rolls is an inconsistency in positioning the rear of truck beds with respect to feed hoppers. Such inconsistency is the result of differences in trailing lengths of truck beds, differences in the lengths by which truck beds extend rearward beyond the rear set of tires of such trucks. When repeatability of the dumping position between trucks is desirable, such inconsistencies present a problem.